Corner watering system for center pivot irrigation machines

ABSTRACT

A center pivot irrigation machine having a swing arm for irrigating corner areas of a field. The swing arm has a steerable support tower which follows a buried cable to guide the swing arm into and out of the field corners. A double hinge connection between the main irrigation boom and the swing arm includes one hinge joint which accommodates pivoting of the swing arm and another hinge joint which controls the operation of the tower drive motors. A cam switch monitors the steering angle of the swing arm tower and turns the sprinklers of the swing tower on and off in accordance with the steering angle to achieve uniform water application. A secondary set of sprinklers on the main boom is deactivated and the entire machine is slowed when the steering angle indicates that the swing arm is covering a rapidly increasing area.

This is a division of application Ser. No. 363,275, filed Mar. 29, 1983.

BACKGROUND OF THE INVENTION

This invention relates generally to irrigation equipment and moreparticularly to a center pivot irrigation machine which is provided witha swing arm attachment for irrigating corner areas of fields.

Although center pivot type irrigation machines have achievedconsiderable popularity and function satisfactorily for the most part,they are capable of watering only circular areas. The basic center pivotmachine is not able to irrigate the corner areas of square fields orother areas outside of the circle covered by the machine. Various typesof attachments have been proposed to more adequately cover the sizeableland area represented by the field corners. To date, the most successfultype of "corner system" is known as a swing arm or swing span.

The swing arm is essentially an end span similar to the remainder of theirrigation machine except that it has a hinge connection with one end ofthe main boom and is supported by a tower having steerable wheels. Asthe main boom turns about the central pivot stand, the steerable towerfollows a buried cable or other guide device which causes the swing armto pivot out into the corners of the field and to retract back behindthe main boom as the system departs from a corner. In this manner, theswing arm system provides an extension boom which is able to cover agood part of each corner of the field. The known prior art relating toswing arm corner systems includes U.S. Pat. Nos. 3,797,517 to Kircher etal, 3,802,627 to Seckler et al and 3,902,517 to Daugherty et al.

All of the swing arm corner systems that have been proposed in the pastfail to apply water in a uniform manner to the corners of the field. Asthe swing arm folds out into the corner, it travels faster than thesystem as a whole, and the area covered by the swing arm during itsextension is underwatered. Conversely, the swing arm moves relativelyslowly as it retracts out of the corner, and over watering occurs in theareas covered by the swing arm as it folds back behind the main boom.The overall result is that some areas near the field corners areunderwatered and other areas are overwatered, and the effectiveness ofthe irrigation suffers accordingly.

The uniformity of the water pattern also suffers due to the changes thatoccur in the effective overall length of the irrigation system as theextension boom folds out and then back in. In order to apply waterevenly, it is necessary to supply water to the machine at varying ratesbecause much more water is required when the machine is operating at itsmaximum length than when it is at minimum length. For example, if theeffective length of the system is 1280 feet with the swing arm fullyretracted and 1545 feet with the swing arm fully extended, the waterrequirements are over 30% less in the retracted mode of operation thanin the fully extended mode (when an end gun is included).

The need to provide varying amounts of water to the system detracts fromthe efficiency of the pumping equipment and the supply network. Also,the water supply must operate at much less than full capacity themajority of the time since full capacity is required only when the swingarm is fully extended. Even if the water supply has sufficient capacityto irrigate the total coverage area of the irrigation system, it maynevertheless be inadequate in actual practive because it must operatemost of the time at 70% or less capacity. This makes many marginal wellsimpractical for use with the irrigation machine.

Efficiency of swing arm machines is dependent largely upon accurateguidance of the extension boom and effective control of the steeringaction and the speed of both the main and the extension booms. In thepast, the extension boom has been attached to the end of the main boomby means of a hinge that permits the extension boom to swing in and outand a separate sliding mechanism that allows relative linear motionparallel to the extension boom. The linear motion is needed to operateswitches that stop the tower of the swing arm when it moves too farahead and to stop the last tower of the main boom if necessary to permitthe swing arm tower to catch up. In addition to the cost and difficultyinvolved in constructing a suitable sliding mechanism, it is notuncommon for devices of this type to either slide erratically orcompletely bind. Consequently, the control arrangement operated by thesliding mechanism is subject to malfunction.

The end boom section which extends beyond the tower of the swing arm istypically supported by rods or cables extending to its outer end from amast forming a vertical extension above the steerable tower. It isnecessary to anchor the mast in a vertical position by supports such astruss rods or cables. If the boom section is relatively long and heavy,the truss rods or cables distort the shape of the swing span. In orderto avoid this distortion, the rods or cables are sometimes extended backthe full length of the swing span, thus increasing the material costsand detracting from the appearance of the structure.

SUMMARY OF THE INVENTION

The present invention is aimed at eliminating or reducing theaforementioned drawbacks associated with the known swing arm cornersystems. It is an important object of the invention to provide animproved corner watering system that applies water to the corner areasof the field more uniformly than is achieved with the devices that havebeen proposed in the past. In accordance with the invention, the areasof overwatering and underwatering are significantly reduced by properlycontrolling the sprinklers on the extension boom. Since the rate ofchange in the area that is being covered by the extension boom isrepresented by the angulation of the wheels of the steerable tower, thissteering angle is monitored and the sprinklers are turned on and off inaccordance with the steering angle in a sequence that achievessubstantially uniform water application as the extension boom pivotsinto and out of the corner areas of the field. The steering angle alsocontrols the speed of the system in an indirect manner by slowing themain boom down when the extension boom is extending and speeding themain boom up when the extension boom is retracting. As a result,compensation is made for the head variation and the length changes thatoccur in the corner areas of the field, and a substantially uniformamount of water is applied to all areas of the field covered by theirrigation machine.

Another important object of the invention is to provide a cornerwatering system having increased hydraulic efficiency. The main boom hastwo sets of sprinklers arranged in alternating fashion, and one set isdeactivated when the extension boom has folded out far enough toactivate its sprinklers. The sprinklers on the extension boom are sizedto apply approximately the same amount of water as the deactivatedsprinklers on the main boom, and the total flow rate thus remainssubstantially constant. The entire system is slowed down in the cornerareas of the field to compensate for the increased system length, andthe depth of the water application is thereby maintained relativelyconstant throughout the coverage area of the machine. By operating thesystem at a substantially constant flow rate throughout its operatingcycle, the water supply is used at its highest capacity nearly all ofthe time, and the inefficiencies and other problems associated withvarying flow rates are avoided.

A further object of the invention is to provide, in a corner wateringirrigation system of the character described, an improved mechanism forconnecting the extension boom with the main boom. The double hingearrangement permits the extension boom to pivot as required while alsoproviding the linear motion that is necessary to properly control thetowers. At the same time, the difficulties associated with slidingmechanisms are avoided.

An additional object of the invention is to provide an improved trussstructure for the extension boom. The integrated truss which providessupport for both the span action and the end boom section of the swingarm is more efficient and more attractive than the type of trusses thathave been previously proposed.

Other and further objects of the invention, together with the featuresof novelty appurtenant thereto, will appear in the course of thefollowing description.

DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which form a part of the specification andare to be read in conjunction therewith and in which like referencenumerals are used to indicate like parts in the various views:

FIG. 1 is a diagrammatic plan view of a center pivot irrigation machinehaving a corner watering system constructed according to the presentinvention and showing the path of movement of the extension boom in onecorner area of the field;

FIG. 2 is a fragmentary side elevational view of the extension boom ofthe irrigation machine;

FIG. 3 is a fragmentary top plan view of the extension boom;

FIG. 4 is a fragmentary perspective view showing a portion of the trussstructure on the extension boom;

FIG. 5 is a fragmentary sectional view taken generally along line 5--5of FIG. 4 in the direction of the arrows;

IG. 6 is a fragmentary perspective view of the steerable support towerfor the extension boom;

FIG. 7 is a fragmentary perspective view showing the control box of thesteerable support tower, with a portion of the box broken away toillustrate the cam arrangement which monitors the steering angle;

FIG. 8 is a top plan view of the control box shown in FIG. 7, with aportion broken away for purposes of illustration;

FIG. 9 is a fragmentary perspective view of the double hinge structurewhich connects the extension boom with the end of the main boom;

FIG. 10 is a fragmentary top plan view of the double hinge structureshown in FIG. 9, with the broken lines indicating movement of theextension boom about both hinge axes;

FIG. 11 is a fragmentary elevational view of the control box of thedouble hinge, with a portion broken away to illustrate the internal camand switch arrangement;

FIG. 12 is a perspective view illustrating one of the secondarysprinklers on the main irrigation boom;

FIG. 13 is a perspective view illustrating one of the sprinklers on theextension boom;

FIG. 14 is a schematic diagram of the control system for the sprinklerson the extension boom;

FIG. 15 is a schematic diagram of the control system for the secondarysprinklers on the main irrigation boom;

FIG. 16 is a schematic diagram of the electrical circuit for thecollector ring at the pivot point of the irrigation machine;

FIG. 17 is a circuit diagram of the primary percent timer on the maincontrol panel of the irrigation machine;

FIG. 18 is a schematic diagram of the electrical circuit in the controlbox of the hinge tower;

FIG. 19 is a schematic diagram of the electrical circuit on thesteerable tower of the extension boom;

FIG. 20 is a diagrammatic view illustrating typical steering angles ofthe steerable support tower during extension and retraction of the swingspan.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings in detail and initially to FIG. 1, acenter pivot irrigation system constructed in accordance with thepresent invention includes a main boom 10 which pivots about a pivotstand 12 located at one end of the boom. Conventional support towers 14support the main boom 10 at an elevated position above the field whichis to be irrigated. The towers 14 have wheels that are driven in aconventional manner by electric drive motors (not shown), and the towersare maintained in a substantially straight line by a suitable alignmentsystem of the type normally provided on center pivot machines. Water ispumped into boom 10 from a well and is applied to the field bysprinklers which will be discussed in more detail.

The main boom 10 covers a circular area of the field which is centeredat the pivot stand 12. The boundary of the circular area covered by boom10 is indicated at 16 in FIG. 1.

In accordance with the present invention, a swing arm corner system forirrigating the corner areas of the field includes an extension boom 18which is pivotally connected with the outer end of the main boom 10. Thepivotal connection is located adjacent to an outer tower 20 of the mainboom which is referred to as the hinge tower. The extension boom 18 issupported on a steerable tower 22 which is referred to as the swingtower. Guidance of the extension boom 18 through the corners of thefield is controlled by a buried cable 24 which is followed by thesteerable swing tower 22, as will be more fully explained. The buriedcable 24 is arranged in an arcuate pattern in the corners of the fieldso that the extension boom will swing out as the main boom approachesthe corners. The cable is arranged in a predetermined and systematicallymeasured line along the sides of the field so that the extension boomwill fold back inwardly behind the main boom along the sides of thefield.

The details of the extension boom 18 are best shown in FIGS. 2-5.Between towers 20 and 22, the extension boom has a span 6 which isformed by a plurality of pipes 28 connected end to end with one another.A cantilevered end boom section 30 located outwardly of the swing tower22 is formed by smaller diameter pipe sections 32 also connected end toend with one another. A relatively short pipe section 34 is mounted ontop of tower 22 and connects span 26 with the end boom section 30.

Span 26 is bowed upwardly somewhat and is provided on its underside witha truss formed by a plurality of V braces 36 extending outwardly anddownwardly from the pipe sections 28. The V braces 36 in each pair areconnected at the bottom by cross braces 38 (see FIG. 3). A pair of trussrods 40 connect with the vertices of the V braces 36 and with the span26 at their opposite ends. Side loads applied to the swing tower 22 areresistant by horizontal braces 42 which are stabilized by shorter braces44 connecting with the boom. Another pair of braces 46 extend frombraces 42 to connection with the extension boom at a location adjacentthe swing tower 22. V braces 47 provide further bracing.

Forming a vertical extension of tower 22 is a mast 48 carrying on itstop end a horizontal bar 50. The opposite ends of bar 50 are located onopposite sides of the extension boom 18. Truss rods 52 connect with theopposite ends of bar 50 and extend downwardly and inwardly to connectionwith the outer end portion of the end boom section 30. The rods 52 formthe upper chords of a truss having boom section 30 as its lower chordand a plurality of inverted V braces 54 as the web members. Each V brace54 connects with one of the truss rods 52 at its apex and with boomsection 30 at the opposite end. Cross braces 56 extend between theapices of the V braces in each pair.

The truss structure also includes a pair of truss rods 58 which extendfrom the opposite ends of bar 50 to connection with span 26 at a flange60 located between two of the pipe sections 28. Another pair of trussrods 62 extend from the opposite ends of bar 50 to connection withanother flange 64 at the approximate midpoint of span 26. An inverted Vbrace 66 (FIGS. 4 and 5) connects with an intermediate portion of rod62. A cross brace 67 extends between the V braces 66. Rods 62 serve asstiffeners which stiffen the structure and prevent distortion of theextension boom as it is being filled or emptied.

Truss rods 52 and V braces 54 are chosen so that the end boom section 30is substantially straight when it is filled with water. The web membersformed by V braces 54 transfer the weight of the pipe to truss rods 2.The truss rods form a smooth, segmented curve when the extension boom isfilled with water. The location of flange 60 is such that the bendingmoment applied to it by the end boom section 30 is counterbalanced bythe opposite bending moment applied by the span 26. Thus, flange 60 isat a point of zero bending moment, and the weight of span 26 inwardly offlange 60 is counterbalanced by the weight of the end boom section 30.Therefore, the truss structure make it possible to use either a longerspan betwen towers 20 and 22 and/or lighter truss members.

Referring now to FIG. 6 in particular, the steerable swing tower 22includes a pair of legs 68 which converge as they extend upwardly andconnect with the extension boom 18 at their upper ends. A bracket 70connects the short pipe section 34 of the extension boom to legs 68.Bracket plates 72 connect the bottom ends of legs 68 with a generallyhorizontal base 74 of the tower. The opposite ends of base 74 connectwith vertical sleeves 76.

Each sleeve 76 receives a leg 78 carrying a ground engaging wheel 80 onits lower end. Each leg 78 has a conventional electric motor 82 whichdrives the corresponding wheel 80 through a gear box 84. Legs 78 areable to turn in sleeves 76 in order to steer the swing tower 22.

Steering is controlled by a steering motor 86. The steering motor islocated in a box 88 mounted on an arm 90 extending upwardly from one ofthe sleeves 76. Motor 86 drives a gear box 92 which is mounted to aflange 94 of a steering arm 96. Flange 94 is also bolted to the top ofleg 78 so that leg 78 turns in sleeve 76 to provide steering action whenmotor 86 is activated. The other leg 78 is bolted to a flange 98 ofanother steering arm 100 oriented parallel to arm 96. The two steeringarms 96 and 100 are connected by a tie rod 102 which causes both wheels80 to be steered in the same direction.

Referring now to FIGS. 7 and 8 in particular, the steering angle ofwheels 80 is monitored by a cam operated switch mechanism located withina control box 104. The control box 104 is mounted on top of arm 106secured to one of the sleeves 76. Extending upwardly into box 104 fromflange 98 is a vertical shaft 108 carrying a pulley 110 on its top end.A cog belt 112 is drawn around pulley 110 and around another pulley 114carried on a shaft 116. Shaft 116 also carries a plurality of cams 118that control corresponding switches 120. As will be explained morefully, there are seven cams that control the irrigation machine inaccordance with the steering angle of wheels 80 with respect to theextension boom.

The pivotal connection between the main boom 10 and the extension boom18 is effected by the double hinge arrangement shown in FIGS. 9 and 10.The hinge tower 20 has a pair of upwardly converging legs 122 thatconnect at their top ends with a bracket 124. Connected to the bracketis an elbow 126 having a flange connection 128 with the outer end of themain irrigation boom 10. The vertical portion of elbow 126 extendsthrough a plate 130 forming an arm of the hinge assembly. Plate 130 issupported to turn on the elbow by suitable rollers 131. A swivelcoupling 132 connects with the lower end of elbow 126 and is clamped toa vertical hose 134 by hose clamps 136. A U shaped tube 138 is clampedat one end to hose 134 and at the opposite end to another vertical hose140. Hose 140 is in turn clamped to an elbow 142 having a flangeconnection 144 with the inner end of the extension boom 18. The flexibleV shaped hose arrangement permits water to flow to the extension boom 18from the main boom 10.

A first hinge connection is formed by a ball joint 146 locatedimmediately above and aligned with hose 134. The turning portion of theball hitch 146 is carried on an arm 148 extending to connection with apair of bracket plates 150 mounted on plate 130 at a location offsetfrom the hinge axis. An intermediate portion of arm 148 connects with abracket 152 secured to plate 130. The vertical hinge axis provided bythe ball joint 146 permits the extension boom 18 to pivot into and outof the corner areas of the field that is being irrigated.

An outer hinge axis is provided by a ball joint 154 located on the outerend of plate 130. A ball is mounted on plate 130 and the turning portionof the joint is carried on an arm 156 extending from elbow 142.

The drive motors of the hinge and swing towers are controlled inaccordance with the angular position of the extension boom about theouter hinge joint 154. An L shaped arm 158 has a horizontal portionsecured to lugs 160 mounted on plate 130. The top end of arm 158 carriesa bracket 162 having parallel rods 164 hooked to its opposite ends. Theother ends of rods 164 are hooked to the opposite ends of anotherbracket 166 located above the elbow 142 and parallel to bracket 162.Extending upwardly from the center of bracket 166 is a shaft 168.

As best shown in FIG. 11, shaft 168 enters the bottom of a control box170 mounted adjacent the flange connection 144. Carried on shaft 168within box 170 are a plurality of cams 172 which control correspondingswitches 174. The cams 172 and switches 174 control the drive motors ofthe hinge tower 20 and swing tower 22 in a manner that will be describedmore fully.

FIG. 14 schematically shows a series of sprinklers which are spacedalong the length of the extension boom 18 and numbered consecutivelyfrom its inner end to its outer end. Each sprinkler on the extensionboom has a valve, and the sprinkler valves are controlled by solenoidpilot valves numbered 1-7 and contained within a valve box 176 mountedon top of the swing tower 22. Water is supplied from the extension boomto the pilot valves, and each pilot valve has a control line connectingwith selected sprinkler valves. For example, the No. 1 pilot valve has acontrol line that leads to sprinkler valve Nos. 5, 13, 21 and 29. Pilotvalves 1-6 are normally closed solenoid valves that open when suppliedwith electric current, while the No. 7 valve is a normally open solenoidvalve that closes when supplied with electric current. The No. 7 pilotvalve controls the valve for the high volume end gun 178 mounted on theouter end of the extension boom.

FIG. 13 depicts the No. 4 sprinkler structure. A pipe nipple 180 isthreaded into a water outlet 182 on top of boom 18. Threaded on top ofthe pipe nipple is a water control valve 184 that connects with thecontrol line 186 leading from the previous sprinkler assembly which inthis case is the No. 8 sprinkler (see FIG. 14). A strainer 188 islocated on top of valve 184 and receives a riser 190 and a sprinkler 192which applies water to the field when activated. The No. 4 sprinklerassembly controls some of the sprinklers on the main boom 10 and forthis purpose has a control line 194 extending from the strainer 188.Valve 184 and the remaining sprinkler valves are normally open valvesthat normally supply water to the sprinkler 192. However, when waterpressure is applied to the control line 186, valve 184 closes to cut offthe water supply to the sprinkler.

Referring to FIG. 15, the main boom 10 includes a set of primarysprinklers 196 and a set of secondary sprinklers 198. The primary andsecondary sprinklers are arranged in alternating fashion along thelength of the main boom. The primary sprinklers 196 are activated at alltimes, while the secondary sprinklers 198 are normally activated but aredeactivated when pressure is applied to their associated valves by thecontrol line 194 leading from the No. 4 sprinkler assembly on theextension boom. The control line 194 is provided with manual drainvalves 200 located on the support towers 14 of the main irrigation boom.

FIG. 12 illustrates the structure of each of the secondary sprinklers198. A pipe nipple 204 is threaded into a connection 206 on top of themain boom 10. A normally open valve 208 is threaded onto the pipe nippleand receives a riser 210 leading to a sprinkler 212. The control line194 connects with valve 208 and continues on to connection with thevalves of the remaining secondary sprinklers. When the No. 4 sprinkleron the extension boom is activated, it applies water pressure to line194 and thereby closes all of the valves 208 of the secondarysprinklers. When the pressure on line 194 is relieved, valves 208 areopen to provide water to the sprinklers 212. The numbered sprinklers onthe extension boom 18 are constructed similarly to the sprinkler shownin FIG. 12, except that the No. 20 sprinkler differs in that it has astrainer below the valve.

With reference again to FIG. 6, the swing tower 22 is provided with twosensors 214 and another sensor 215 mounted on an elongate horizontal arm216. Arm 216 is mounted to a pair of brackets 218 which are secured toone of the tower legs 78. The sensors are null sensing devices thatrespond to the signal from the buried cable 24 (FIG. 1) to control thesteering motor 86 in a manner to guide the swing tower 22 along the pathprovided by the cable 24. The mounting of sensor 214 on an arm extendingahead of the wheel 80 allows it to smooth out small curves in the pathprovided by cable 24. The smooth and accurate steering action providedby this arrangement is important in achieving effectiveness in thesteering angle control system, as will be explained more fully.

The operation of the sprinklers and the drive motors for the supporttowers is controlled by an electrical system which is shownschematically in FIGS. 16-19. Referring first to FIG. 17, the maincontrol panel of the irrigation machine has an adjustable percent timer220. The percent timer includes a coil 222 and a switch 224 controlledby the coil. One hundred twenty volts is applied to coil 222. Thepercent timer 220 can be set to effect closing of switch 224 for thepercentage of time it is desired for the drive motors to operate duringeach period of the operating cycle of the timer. For example, if thepercent timer 220 is set at 50 percent and there is a one minute timecycle, switch 224 is closed for 30 seconds of each minute and open forthe other 30 seconds. When switch 224 is closed, 120 volts is applied toa conductor 226 which extends through a conduit 228 along withadditional conductors.

Referring now to FIG. 16, conduit 228 leads to a collector ring assembly230 located at the pivot stand 12 of the irrigation machine. Thecollector ring assembly 230 supplies electrical power to the rotatingirrigation boom. The conductor 226 which is controlled by the percenttimer 220 connects with another conductor 232 leading from the collectorring. Line 232 extends into a conduit 234 which leads to a control boxon each support tower of the main boom, including the hinge tower 20.Also extending from the collector ring assembly through conduit 234 areconductors 236, 238 and 240 which apply 480 volts to the tower drivemotors. The collector ring assembly also has a ground line 242 extendingthrough conduit 234. A direction switch (not shown) controls theapplication of power to lines 244 and 246. Line 244 receives 120 voltswhen the machine is operating in the forward mode, and the other line246 receives 120 volts in the reverse mode of operation of the machine.

The collector ring assembly 230 has another conductor 248 which isprovided with an end gun switch 250. Line 248 is energized if the endgun switch 250 is closed due to the continuous application of 120 voltsto the end gun switch when the machine is energized. Switch 250 isnormally open and is closed by trip bolts (not shown) at the pivot stand12 when the main boom 10 is in the corner areas of the field. End gunswitch 250 is in series with switch 120g (FIG. 19). Thus, the end gunsolenoid operation can be interrupted regardless of the swing spanposition in the field. The purpose of this arrangement is to avoidwatering an obstacle without folding the boom backwards, thus giving amore precise control of the water application pattern of the swing spanso as to avoid watering undesirable areas such as those occupied bybuildings for example. An automatic stop switch 52 is included in aconductor 254 leading from the collector ring assembly. Conductor 254receives power when the irrigation machine is switched on and isinterrupted whenever the automatic stop switch 252 opens. Also extendingthrough conduit 234 is a neutral line 256 leading from the bank ofcollector rings.

FIG. 18 depicts the circuitry in the control box of the hinge tower 20which is actually mounted on the swing span 18 next to the hinge tower.The conductors leading to the hinge tower control box through conduit234 connect to a terminal strip 258 (or directly to the disconnect insome cases). Lines 236-248 and 256 extend from connector 258 (or fromthe disconnect) back into a conduit 260 that leads to the control boxfor the swing tower 22. The 480 volt lines 236, 238 and 240 connectthrough connector 258 with respect to lines 262, 264 and 266. Theselines have switch contacts controlled by an on/off switch 268 and, whenthe on/off switch is closed, lead to respective normally open relaycontacts 270a, 270b and 270c controlled by a relay coil 270 serving as astarter for a drive motor 272 of the hinge tower. When the relaycontacts are closed, lines 262, 264 and 266 apply 480 volts to motor 272which then propels the wheels of hinge tower 20.

Line 244 connects through connector 258 with another line 274 having acontact of the on/off switch 268. Line 274 connects with one side of adirection relay coil 276 which controls two sets of normally opencontacts 276a and 276b and two sets of normally closed contacts 276c and276d. The neutral line 256 connects through connector 258 with a line278 and that leads to one side of relay coil 270 and also to one side ofcoil 276 and on to relay coil 290. Thus, coil 276 is energized in theforward operating mode of the irrigation machine and is deenergized inthe reverse mode.

The switches 174 controlled by cams 172 are five in number and aredesignated by numerals 174a-174e in FIG. 18. Switches 174a and 174bcontrol the operation of the swing tower drive motors in the bothdirections by acting to latch and unlatch the swing span relay. Switches174c and 174d control the hinge tower drive motor 272 in the forward andreverse modes of operation, respectively. Switch 174e is a limit switchthat opens whatever the outer hinge joint 154 turns in either directionbeyond a preselected limiting position.

Line 232 connects through connector 258 with a line 280 having one ofthe contacts of the on/off switch 268. Line 280 connects with one sideof each set of contacts 276a-276d of the direction relay. Contacts 276aconnect on their opposite side with a line 282 leading to switch 174c.Contacts 276c connect on their opposite side with a line 284 leading toswitch 174d. The opposite sides of contacts 276b and 276d connect withrespective lines 286 and 288 leading to a relay 289 that controls theoperation of the swing tower drive motors. The relay 289 includes a coil290 which controls two sets of normally open contacts 290a and 290b andtwo sets of normally closed contacts 290c and 290d. Lines 286 and 288connect with contacts 290a and 290c, respectively. The opposite sides ofcontacts 290a and 290c connect with a line 292 leading to connectionthrough connector 258 with a conductor 294 that extends through conduit260 to the swing tower.

Line 254 connects through connector 258 with a line 296 leading to thelimit switch 174e. Extending between the opposite side of switch 174eand one side of switch 174a is a conductor 298. Another conductor 300connects with line 298 and extends through one contact of switch 268 tothe connector 258. The connector provides a connection between line 300and another line 302 that leads through conduit 260 to the swing tower.

The side of switch 174a opposite line 298 connects with a line 304 thatalso connects with switch 174b and one side of normally open contact290b. The opposite side of contact 290b connects with a line 306 leadingto one side of the relay coil 290. The opposite side of coil 290connects with the neutral line 278. Line 308 connects at one end withline 306 and at the opposite end with one side of switch 174b.

FIG. 19 illustrates the control circuitry that operates the swing towerdrive motors, sterring motor and sprinklers, although the circuitry inthe "H-box" (FIG. 18) can interrupt the swing tower drive motors and thesteering motor. The conduit 260 leading from the hinge tower extends toa control box 310 mounted on the swing tower 22. The conductors thatextend within conduit 260 lead to the contacts of an on/off switch 312.The 480 volt conductors 236, 238 and 240 connect with the drive motors82 of the swing tower through contacts of switch 312 and normally opencontacts 314a, 314b and 314c. A tower starter coil 314 closes contacts314a, 314b and 314c when energized.

Conductors 236, 238 and 240 also connect through the contacts of switch312 with the steering motor 86. The direction the steering motor 86 isdriven is controlled by steer in and steer out starters 316 and 318,respectively. The steer in starter 316 controls normally open contacts316a, 316b and 316c, and the steer out starter controls normally opencontacts 318a, 318b and 318c. When the steer in starter 316 isenergized, its contacts close and 480 volts is applied to drive motor 86in a direction to steer the tower wheels 80 in so that the extensionboom 18 is retracted. Conversely, when the steer out starter 318 isenergized, its contacts close and the 480 volt lines apply power tomotor 86 in a manner to steer wheels 80 outwardly to effect extension ofboom 18.

Line 244 leads to one contact of switch 312 and makes power available tothe contact of a multiple contact relay 320 in the forward mode ofoperation. Line 246 also connects with one contact of switch 312, and inthe reverse mode of operation, makes power available to the coil ofrelay 320 and to the coil of another multiple contact relay 322. Line246 also leads to connection with a receiver 324 which receives signalsfrom the two sensors 214 and from sensor 215.

Line 302 includes a contact of switch 312 and connects with receiver 324through a normally closed limit switch 326. The receiver 324 includes aset of normally open contacts 324a and a set of normally closed contacts324b. When contacts 324a are closed, line 302 is connected with a line328 that connects with relay 320 and with the switch assembly 120 thatis controlled by the steering angle of the swing tower wheels.

The switch assembly 120 includes seven switches 120a-120g which areactivated in sequence with increasing steering angle. Line 238 providespower to one side of each switch 120a-120f. The opposite sides ofswitches 120a-120f normally connect with respective conductors 330a-330fthat lead through a conduit 332 to a connector 334 located within thepilot valve box 176. Line 330a connects through connector 334 with oneside of the normally closed No. 1 pilot valve 336a, and the remaininglines 330b-330f connect through the connector with a normally closed No.2-6 pilot valves 336b-336f, respectively. The opposite side of eachvalve 336a-336f connects through connector 334 with a neutral line 338.

Line 248 connects through one contact of switch 312 with a conductor 340leading to one side of the No. 7 switch 120g. When switch 120g isactivated, its opposite side connects with a line 330g that extendsthrough conduit 332 and connects through connector 334 with one side ofthe normally open No. 7 pilot valve 336g. The opposite side of valve336g connects with the neutral line 338.

Line 294 includes one of the contacts of the on/off switch 312 andconnects with a set of normally open relay contacts 342a and a set ofnormally closed contacts 342b. The contacts 342a and 342b are controlledby a relay coil 342. Line 294 also connects with a the contacts of asecondary percent timer 344 having a coil 346 which controls a switch348. Line 294 connects with one side of the switch 348, and the otherside of the switch connects with a line 350 that normally connects withline 294 through the normally closed contacts 342b. Extending betweenline 350 and the tower starter coil 314 is a conductor 352. The oppositeside of the tower starter 314 connects with a neutral return line 354that also connects with the steer in and steer out starter overloadcontacts 316 and 318. One side of coil 346 connects with a neutral line356, and the other side of the coil connects with a line 358 that leadsto the normally open relay contacts 342a.

The secondary percent timer 344 is similar to the primary percent timer220 on the main control panel. When the coil 346 is energized, switch348 remains closed for a preselected number of seconds of each minute.For example, if the secondary percent timer is set at 50 percent, switch348 is closed for 30 seconds out of every minute that coil 346 isenergized. Power is applied to relay coil 342 along a conductor 360.Conductor 360 is normally interrupted but connects with line 328 whenthe No. 4 cam operated switch 120d is tripped.

In the forward mode of operation, relays 320 and 322 are deenergized,and power is available to the steer in starter 316 through receiver 324along line 362, switch 322a, line 364, line 365, steering switch 366,line 368, switch 320a, and line 370. Power is likewise available to thesteer out starter 318 through the receiver along line 372, switch 322b,line 374, line 375, steering switch 376, line 378, switch 322c, and line380. In the reverse mode of operation, relays 320 and 322 are energizedand power is available to the steer in motor 316 through receiver 324along line 362, switch 322a, line 375, switch 376, line 378, switch320a, and line 370. Power is available to starter coil 318 through thereceiver along line 372, switch 322b, line 365, switch 366, line 368,switch 322c, and line 380. Thus, the steer in and steer out starters 316and 318 are controlled by the sensor 214 such that motor 86 steers theswing tower along the path defined by the buried cable 16.

In operation of the irrigation machine, water is pumped into the mainirrigation boom 10 from a well or other suitable source (not shown). Thedrive motors for the support towers 14 of the main boom propel itthrough the field in the usual circular path. As boom 10 travels alongthe sides of the field, the extension boom 18 is folded back behind it.Since all of the sprinklers on the extension boom 18 are deactivated(including the No. 4 sprinkler), the control line 194 (FIG. 15) is notpressurized, and both sets of sprinklers 196 and 198 of the main boom 10are activated. The sprinklers thus apply water along the length of themain boom 10 as it travels through the field. The conventional alignmentsystem (not shown) of the main boom maintains towers 14 in alignmentwith one another and also maintains the hinge tower 20 in alignment withthe remaining support towers 14 to maintain the main boom in asubstantially straight condition.

As the main boom 10 approaches a corner area of the field, the extensionboom 18 folds out into the corner of the field and then retracts backbehind the main boom as it departs from the corner area, as best shownin the broken line views of FIG. 1. The leading sensor 214 picks up thesignal emitted by the buried cable 24 and controls the steering motor 86such that the swing tower 22 follows the path defined by the cable. Asthe extension boom 18 is being steered outwardly or inwardly about theinner hinge connection 146, the cams 118 monitor the steering angle ofwheels 80 with respect to the axis of the extension boom 18, and theswitch assembly 120 is controlled accordingly. As the steering angleincreases, switches 120a-120g are tripped in succession. When switch120a is tripped, power is removed from line 330a and the normally closedNo. 1 pilot valve 336a closes. As shown in FIG. 14, the water pressureapplied to the valves of sprinklers 5, 13, 21 and 29 is then relieved,and these four sprinklers of the extension boom are activated to beginapplying water to the corner area of the field. When the steering angleis relatively small, the effective area covered by the extension boom isrelatively small, and only a small number of sprinklers, (i.e. 4) areneeded to adequately irrigate the corner area of the field.

As the steering angle increases during extension of the extension boominto the corner area of the field, the extension boom covers increasingarea, and additional sprinklers are activated in a preselected sequence.When the No. 2 switch 120b is tripped, valve 336b closes and sprinklers1, 9, 17 and 25 are activated. The remaining switches 120c-120g aretripped in sequence with increasing steering angle, and all of thesprinklers on the extension boom are activated when the steering angleof the swing tower is maximum and the extension boom 18 is coveringmaximum area.

The last switch that is tripped is the No. 7 switch 120g which thencloses the normally open No. 7 pilot valve 336g. Since the end gunswitch 250 (see FIG. 16) is arranged in series with switch 120g, it isnecessary for both switches 250 and 120g to be closed in order to closethe number seven pilot valve 336g in order to activate the large volumeend gun 178. Since the end gun control is shared by the trip boltoperated end gun switch 250 located at the pivot stand and the camcontrolled switch 120g of the swing tower, the end gun is activated anddeactivated at the most advantageous times for proper water application.If desired, more than one end gun can be controlled in the same fashionto improve the water pattern at the outer end of the irrigation machine.

When the wheels 80 of the swing tower are steered approximately halfwayout or halfway to the maximum steering angle, the No. 4 switch 120d istripped. At this time, the No. 4 sprinkler on the end boom is activatedas shown in FIG. 14. Referring additionally to FIG. 15, activation ofthe No. 4 sprinkler results in the application of water pressure to thecontrol line 194 leading to the secondary sprinklers 198 on the mainboom 10. The secondary sprinklers 198 are then deactivated as theprimary sprinklers 196 continue to apply water to the field. Thus, asthe sprinklers on the extension boom are activated, the secondarysprinklers on the main boom are deactivated. The sprinklers on theextension boom are sized so that the rate at which they discharge wateris approximately equal to the rate at which the secondary sprinklers 198apply water when activated. Consequently, the total flow rate remainssubstantially constant, and considerable hydraulic efficiencies areachieved. Use of the water supply is maximized since it is used at itshighest capacity nearly all of the time.

As the extension boom folds out, the effective length of the irrigationmachine increases, and the machine is automatically slowed down tocompensate for the increased area of water application. Normally, line294 controls the drive motors 82 of the swing tower under the control ofthe primary percent timer 220 (FIG. 17). Line 294 normally connectsthrough contacts 342b with line 352 which leads to the tower startercoil 314, thereby energizing the drive motors 82 when the percent timerswitch 224 is closed. However, when the extension boom has folded outfar enough to trip the number four switch 120d, power is applied to line360 for energization of relay coil 342. Contacts 342b then open andcontacts 342a close to provide a current path from line 294 to coil 346.The only available current path to the tower starter 314 is along line294 and through the secondary percent timer switch 348 to lines 350 and352. The secondary percent timer 344 is thus brought into the swingtower control circuit in series with the primary percent timer 220. Thesecondary percent timer is preferably set at a percentage to effectivelyreduce the primary percent timer to approximately 60% of its setting.Slowing of the swing tower 22 results in slowing of the hinge tower 20and the remainder of the irrigation machine, as will be explained morefully, and compensation is thereby made for the increased system lengthas the extension boom folds out into the corner areas of the field.Slowing of the main boom 10 also compensates for the reduced rate ofwater application when the secondary sprinklers 198 are deactivated.

As the main boom 10 continues past the position shown in solid lines inFIG. 1, it begins to depart from the corner of the field, and theextension boom 18 begins folding back behind the main boom. During theretraction stage of operation, the cams 118 continue to monitor thesteering angle of the swing tower wheels 80 and deactivate thesprinklers of the extension boom in reverse sequence as the steeringangle decreases. When the swing tower wheels are steered approximatelyhalfway in, the No. 4 switch 120d moves back to the position shown inFIG. 19 to remove power from line 360, thereby deactivating relay coil342 and removing the secondary percent timer 344 from the controlcircuit. The machine then speeds up since the drive motors arecontrolled solely by the primary percent timer 220. At the same time,the No. 4 sprinkler on the extension boom is deactivated, and thesecondary sprinklers 198 are then activated due to the removal of waterpressure from the control line 194. When the main boom 10 has movedcompletely out of the corner area of the field, the extension boom 18 isfully retracted and all of the switches 120a-120g are in the positionsshown in FIG. 19 to deactivate all of the sprinklers on the extensionboom. The extension boom remains fully retracted along the side of thefield and begins to extend again as the main boom approaches the nextcorner area of the field.

Control of the secondary percent timer 344 in accordance with thesteering angle provides effective control of the overall machine speed.The secondary percent timer, when in the control circuit, directlycontrols the speed of the swing tower 22 to assure that it moves at theproper speed to uniformly apply water to the field corners. The hingetower 20 is in turn controlled by the swing tower speed, due to thelimit switches 174, and the alignment system of the main boom 10controls the support towers 14 from the hinge tower. Accordingly, thespeed of all towers is controlled by the swing tower during someintervals of swing tower operation. When the swing span is fullyretracted the hinge tower is not interrupted by the swing tower.

It is again pointed out that the cams 118 which control switches120a-120g monitor the steering angle of the swing tower wheels ratherthan the angle between the main and extension booms. The steering angleis a measure of the rate at which the swing span is extending orretracting and is thus an accurate measure of the change in the areathat is being covered by the swing span. For example, FIG. 20illustrates that with the extension boom 18 oriented at 140° relative tothe main boom 10, the steering angle is considerably different dependingupon whether the extension boom is being extended or retracted. Duringextension, the steering angle is about 85°, and the increase in the landarea that is being covered by the extension boom is relatively great.Accordingly, it is desirable for uniform water application to activate alarge number of sprinklers. During retraction, the steering angle isapproximately 60°, and there is a relatively small rate of change in thearea that is being covered by the extension boom. Consequently, arelatively small number of sprinklers should be activated in order toprevent overwatering of this area of the field. By controlling thesprinkler operation in accordance with the steering angle, significantoverwatering and underwatering of portions of the field corner isavoided.

As the extension boom 18 swings inwardly and outwardly, it pivots aboutthe vertical hinge axis provided by the inner hinge joint 146. The innerand outer hinge joints 146 and 154 cooperate to permit linear motionparallel to the extension boom 18 in order to properly control the drivemotors of the hinge tower 20 and the swing tower 22. Referring to FIG.18, the hinge tower starter coil 270 is normally energized under thecontrol of the primary percent timer 220 (see FIG. 17). The line 232leading from the primary percent timer connects with line 280 which, inthe forward mode of operation, connects through contacts 276a with line282 since coil 276 is then energized to close contacts 276a. Line 282connects with coil 270 through switch 174c and line 307, and the startercoil 270 then closes its contacts 270a-270c to complete the 480 voltcircuits to the hinge tower drive motors 272.

If the hinge tower 20 begins moving too far ahead of the swing tower 22,the hinge tower pulls plate 130 in a counterclockwise direction aboutthe outer hinge connection 154 as viewed in FIG. 10. The control linkageprovided by brackets 162 and 166 and rods 164 then turns shaft 168 suchthat one of the cams 172 opens switch 174c. The connection between lines282 and 307 is then broken, and starter 270 is deenergized to shut offthe hinge tower drive motors 272, thereby stopping the hinge tower untilthe swing tower has advanced far enough to again effect closing ofswitch 174c. At this time, the hinge tower resumes advancement under thecontrol of the primary percent timer. With the hinge tower stopped, thealignment system on the main boom stops the support towers 14 one afterthe other to maintain the proper alignment.

In the reverse mode of operation, switch 174d similarly controls thehinge tower drive motors 272 in accordance with the angular motion ofthe outer hinge joint 154.

In the forward mode of operation, the swing tower drive motors 82 arelikewise normally controlled by the primary percent timer 220. Withcontinued reference to FIG. 18, the swing span relay coil 290 isnormally energized in the forward mode of operation and is maintainedenergized by the circuit provided by line 296, the limit switch 174e,line 298, switch 174a, line 304, relay contacts 290b, and line 306. Acircuit leading to the drive motors of the swing towers is thencompleted along lines 232 and 280, relay contacts 276b, line 286, relaycontacts 290a, and lines 292 and 294. However, if the swing tower shouldmove too far ahead relative to the hinge tower, the resulting angularmotion about the outer hinge joint 154 is translated by the controllinkage into rotation of the cams 172, one of which opens switch 174a.Lines 298 and 304 are then disconnected to deenergize relay coil 290 andopen contacts 290a to interrupt the connection between lines 286 and292. The swing tower drive motors 82 are thereby shut off until thehinge tower has advanced far enough to again close switch 174a. Switch174b shuts down the swing tower drive motors in a similar fashion in thereverse mode of operation if the swing tower should advance too farahead of the hinge tower.

In this manner, the two hinge connections 146 and 154 cooperate toprovide the required linear motion, while the angular motion about theouter hinge connections 154 is used to properly control the drive motorsof the hinge and swing towers. The double hinge construction providesaccurate control of the towers and eliminates the difficulties involvedin the sliding connections that have been proposed in the past. Thelimit switch 174e of the outer hinge joint is tripped by one of the cams172 to shut down all drive motors if the movement about the outer hingejoint in either direction is excessive.

It is thus apparent that the irrigation machine provided by the presentinvention applies water to the corner areas of a square field moreuniformly than can be achieved by the corner systems that have beenproposed in the past. At the same time, improved hydraulic efficiency isachieved due to the substantially constant flow rate at all stages ofthe operating cycle. The drive motors and sprinklers are controlled inan improved manner, and significant structural improvements are providedby the double hinge arrangement and the integrated truss structure onthe extension boom.

From the foregoing, it will be seen that this invention is one welladapted to attain all the ends and objects hereinabove set forthtogether with other advantages which are obvious and which are inherentto the structure.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

Since many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth are shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

Having thus described the invention, we claim:
 1. In a center pivotirrigation machine having a main boom supported to pivot about one end,an extension boom pivotally coupled with the opposite end of the mainboom, a support tower for said extension boom having steerable wheelsfor pivotally extending and retracting the extension boom relative tothe main boom, a water conduit forming the span of the extension boombetween the main boom and the support tower, and a cantilever end boomsection forming the portion of the extension boom extending beyond thesupport tower, a truss structure for said extension boom comprising:amast extending generally upwardly from the extension boom at a locationadjacent the support tower, said mast having a top portion above theextension boom terminating in opposite ends located on opposite sides ofthe extension boom; a first pair of chords respectively connected at oneend to the opposite ends of said top portion of the mast and at theother end to said end boom section adjacent the outer end thereof toprovide support for said end boom section; a plurality of web membersspaced apart along the length of said end boom section and extendingbetween each chord and said end boom section to cooperate with saidchords in a manner to maintain the end boom section in a substantiallystraight condition when loaded with water, said web members beingarranged to maintain each chord in the shape of a segmented curve whenthe end boom is loaded with water; and a second pair of chordsrespectively connected at one end to the opposite ends of said topportion of the mast and at the other end to said water conduit at apreselected location thereon, said preselected location being chosensuch that when the water conduit and end boom are loaded with water, thebending moments applied to said preselected location by said waterconduit and end boom are substantially equal and opposite to cancel oneanother and provide a point of zero moment at said preselcted location.2. The invention of claim 1, including a pair of elongate stiffenersrespectively connected at one end to the opposite ends of said topportion of the mast and at the other end to said water conduit at alocation spaced inwardly from said preselected location.